Application of fire calorimetry to understand factors affecting flammability of cellulosic material: Pine needles, tree leaves and chipboard
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Date
2012Author
Jervis, Freddy Xavier
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Abstract
Calorimetry, the science of measuring heat from chemical reactions and physical
changes, is one to the most valuable tools fire safety engineering have at their
disposal. Calorimetric devices such as the cone calorimeter and the fire propagation
apparatus (FPA) give us the means to evaluate and understand how different
materials burn at a small scale. Due to fire being affected by many different
environmental factors, these devices help us to isolate and examine how each factor
affects fire as a whole and be able to apply this knowledge to tools that can be used
at larger scales.
This thesis reports various pieces of work on different calorimetric studies done on
cellulosic material used in today’s natural and built environment. All experimental
tests herein are done using the FPA, the state of the art calorimeter for fire safety
studies. The experimental techniques presented here show how invaluable
calorimetry is in giving us key insights on the combustion dynamics of fire related
processes.
The thesis is presented in manuscript style. Each chapter is a stand alone research
work intended for publication with the exception of the first and last chapter;
intended to introduce these and their relevance to the science and the last to
summarize on overall findings and recommended improvements.
Chapter 2 presents a study on the burning of live and dead pine needles. Pine forests
present a relatively high flammability risk comprised in great part by pine needles.
Different moisture content, flow conditions and their interrelationship is studied on
the different parameters affecting the combustion processes. Overall, the results
show that fire physics and chemistry vary with fuel and flow conditions and that
moisture content is not the only difference between live and dead fuels but that the
needle bed physiochemical mechanisms matter as well. This is the first time
calorimetry data is presented on the burning of live and dead pine needles.
Chapter 3 complements chapter 2 with an added in-depth analysis on the effect of
different pine needle species, fuel load and imposed heat insult. Interrelationship
between these variables is shown to have a strong effect on the overall combustion
process. Fuel load is shown to be an essential condition to know as it gives a direct
indication on the intensity of the fire. Flow is shown to have a varied effect
depending on the fuel load, it can either aid or be detrimental to the overall
combustion process especially relating to ignition times.
Chapter 4 is a study on the effect of leaf morphology to flammability of different
natural fuels. This study is a direct extension of the work presented in the paper
Belcher et al (2010) in Nature Geoscience. Representative natural fuel samples from
the Triassic/Jurassic Boundary, a time period of great importance because it marked
a time of major environmental changes, are used to evaluate fire activity as a whole
during this time period. The study shows that smaller leaf area and larger surface
area to volume ratio show a strong correlation to an increase in flammability of these
fuels. The research presents new insight into how leaf morphology can be used as a
tool to assess the effect of fire activity around the globe and how closely vegetation
is linked to this.
Chapter 5 presents a study on flammability of chipboard. Wood being an
inhomogeneous, non-isotropic material presents researchers with a complex problem
due to its burning behavior. Wood has been a preferred construction material since
far back and is widely used in construction today. Different oxygen levels, heat
insults, material thicknesses and densities and the interrelationship between these
variables are assessed to observe the effect on the flammability of chipboard. Density
and thickness is shown to have little effect on the overall burning dynamics with
thermally thick samples apart from the increased fuel content. Oxygen levels and
imposed heat insults, however, show a wide range of effects and the interrelationship
proves to be quite important during the combustion process. The research outlines
how char formation is affected by the different variables and how important this
process becomes along the overall combustion process.
Calorimetric studies are presented that illustrate the use of these devices to study the
effect of varying environmental conditions and the importance of their
interrelationships on both natural and built environment fuels. The works highlight
the importance of first establishing the dynamics of the combustion process in order
to be able to extract combustion parameters that are needed for modeling fires better
in both wildland and built environments.
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